1. Field of the Invention
The present invention relates to a system or method for enhanced auto-ignition in a gasoline internal combustion engine.
2. Description of Related Art
To improve thermal efficiency of gasoline internal combustion engines, lean burn is known to give enhanced thermal efficiency by reducing pumping losses and increasing ratio of specific heats. Flatly speaking, lean burn is known to give low fuel consumption and low NOx emissions. There is however a limit at which an engine can be operated with a lean air/fuel mixture because of misfire and combustion instability as a result of a slow burn. Known methods to extend the lean limit include improving ignitability of the mixture by enhancing the fuel preparation, for example using atomized fuel or vaporized fuel, and increasing the flame speed by introducing charge motion and turbulence in the air/fuel mixture. Finally, combustion by auto-ignition has been proposed for operating an engine with very lean air/fuel mixtures.
When certain conditions are met within a homogeneous charge of lean air/fuel mixture during low load operation, auto-ignition can occur wherein bulk combustion takes place initiated simultaneously from many ignition sites within the charge, resulting in very stable power output, very clean combustion and high thermal efficiency. NOx emission produced in controlled auto-ignition combustion is extremely low in comparison with spark ignition combustion based on propagating flame front and heterogeneous charge compression ignition combustion based on an attached diffusion flame. In the latter two cases represented by spark ignition engine and diesel engine, respectively, the burnt gas temperature is highly heterogeneous within the, charge with very high local temperature values creating high NOx emission. By contrast, in controlled auto-ignition combustion where the combustion is uniformly distributed throughout the charge from many ignition sites, the burnt gas temperature is substantially homogeneous with much lower local temperature values resulting in very low NOx emission.
Engines operating under controlled auto-ignition combustion have already been successfully demonstrated in two-stroke gasoline engines using a conventional compression ratio. U.S. Pat. No. 5,697,332 (=JP-A 7-71279) teaches an exhaust control valve to regulate the pressure in a cylinder during ascending stroke of a piston to achieve auto-ignition combustion of a two-stroke engine at optimum timing. It is believed that the high proportion of burnt gases remaining from the previous cycle, i.e., the residual content, within the engine combustion chamber is responsible for providing the hot charge temperature and active fuel radicals necessary to promote auto-ignition in a very lean air/fuel mixture. Besides, combustion temperature is low due to lean burn, causing a considerable reduction NOx emission. In four-stroke engines, because the residual content is low, auto-ignition is more difficult to achieve, but can be induced by heating the intake air to a high temperature or by significantly increasing the compression ratio.
In all the above cases, the range of engine speeds and loads in which controlled auto-ignition combustion can be achieved is relatively narrow. The fuel used also has a significant effect on the operating range, for example, diesel fuel and methanol fuel have wider auto-ignition ranges than gasoline fuel.
JP-A 11-236848 teaches a first fuel injection at a crank position more than 30 degrees before top dead center (TDC) position of compression stroke and a second fuel injection at a crank position near the TDC position to achieve controlled auto-ignition combustion in a diesel internal combustion engine. At the crank position of the first fuel injection, the temperature in the cylinder is still relatively low so that diesel fuel sprayed as the first fuel injection is not burnt but converted into flammable oxygen containing hydrocarbon due to low temperature oxidation reaction (partial oxidation of hydrocarbon molecules). At the crank position of the second fuel injection near the TDC of compression stroke, the temperature in the cylinder is sufficiently high enough to pyrolyze the gasoline sprayed as the second fuel injection, causing the gasoline to diffuse to make hydrogen due to pyrolysis. The hydrogen burns to elevate the temperature within the cylinder. This temperature elevation causes auto-ignition of flammable oxygen containing hydrocarbon (sprayed gasoline of the first fuel injection). This combustion promotes combustion of the sprayed gasoline of the second fuel injection.
According to this known technique, the injection quantity at the first fuel injection is held below 30% of the maximum injection quantity. Specifically, the injection quantity at the first fuel injection ranges from 10% to 20% of the maximum injection quantity. If the injection quantity at the first fuel injection exceeds 30% of the maximum fuel injection quantity, there occur fuel particles that are heated above the pyrolysis temperature by heat generated during low temperature oxidation reaction of the surrounding fuel., and hydrogen made due to the pyrolysis burns to cause early burn of sprayed gasoline at the first fuel injection. This accounts for why the injection quantity at the first fuel injection is held below 30% of the maximum injection quantity.
Apparently, this technique is intended for use in diesel internal combustion engines. Applying this technique to an auto-ignition gasoline internal combustion engine would pose the following problem.
It is now assumed that the total fuel quantity required per cycle is 60% of the maximum fuel injection quantity. In this case, spraying fuel as much as 10% of the maximum injection quantity at the first fuel injection timing will require spraying fuel as much as 50% of the maximum fuel quantity at the second fuel injection timing. As compared to diesel fuel, it is widely recognized that gasoline fuel is less ignitable, slow in reaction speed of cold temperature oxidation reaction, and least subject to pyrolysis including changes to make hydrogen. Accordingly, the fuel sprayed at the second fuel injection timing will not burn quickly. This sprayed fuel forms fuel rich mixture within a limited region of the combustion chamber, and this fuel rich mixture will burn simultaneously by auto-ignition after low temperature oxidation reaction. Under this combustion condition, increasing fuel quantity of the second injection may cause excessive pressure increase in cylinder and/or increased production of NOx.
JP-A 10-196424 teaches admission of ignition oil to achieve auto-ignition of mixture at or near TDC position of compression stroke. If, as the ignition oil, ignitable fuel is used other than gasoline fuel, dual fuel delivery systems are needed, resulting in increased complexity.
An object of the present invention is to provide a system or method for enhanced auto-ignition in an internal combustion engine.
In carrying out the present invention, a gasoline internal combustion engine is provided. The engine comprises:
a cylinder;
a reciprocating piston disposed in said cylinder to define a combustion chamber therein to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke; and
a fuel injector directly communicating with said combustion chamber for spraying gasoline fuel,
a control arrangement being such that said fuel injector sprays a first injection quantity of gasoline fuel into said combustion chamber at first fuel injection timing, which falls in a range from the intake stroke to the first half of the compression stroke, thereby to form air/fuel mixture cloud that becomes a body of mixture as said piston moves from said first fuel injection timing toward a top dead center position of the compression stroke, and such that said fuel injector sprays a second injection quantity of gasoline fuel into said body of mixture at second fuel injection timing, which falls in the second half of the compression stroke, forming mixture cloud that is superimposed on a portion of said body of mixture, thereby to establish the cylinder content wherein the density of fuel particles within said superimposed portion is high enough to burn by auto-ignition at an ignition point in the neighborhood of the piston top dead center position of the compression stroke, causing temperature rise and pressure, which initiate auto-ignition of the fuel particles within the remaining portion of said body of mixture.
In carrying out the present invention, a system for enhanced auto-ignition management in an internal combustion engine is provided. The system comprises:
a cylinder having a cylinder axis thereof;
a cylinder head closing said cylinder;
a reciprocating piston within said cylinder, said piston, said cylinder and said cylinder head cooperating with each other to define a combustion chamber;
intake and exhaust valves for admitting fresh air into said combustion chamber and for discharging exhaust gas from said combustion chamber, respectively;
a fuel injector mounted to said cylinder head for spraying gasoline fuel into said combustion chamber, said fuel injector having a hollow cone nozzle with a spout communicating with said combustion chamber, said hollow cone nozzle imparting torque to gasoline fuel passing through said spout, causing the fuel to generate swirl around a nozzle axis, promoting the fuel to spread outwardly along a cone surface of an imaginary circular cone, said imaginary circular cone being a solid cone bounded by a region enclosed in a circle and a cone surface that is formed by the segments joining each point on said circle to a point outside of said region and on said nozzle axis within said spout;
said piston moving along said cylinder axis toward and away from said cylinder head to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in cooperation with said intake and exhaust valves; and
a control unit being operative to establish an engine load threshold and an engine speed threshold;
said control unit being operative to compare the engine load with said engine load threshold,
said control unit being operative to compare the engine speed with said engine speed threshold,
said control unit being operative to enable split fuel injection for auto-ignition combustion in response to the comparing result of the engine load with said engine load threshold and the comparing result of the engine speed with said engine speed threshold,
said control unit being operative to determine a ratio in response to the engine load,
said control unit being operative to determine total fuel injection quantity in response to the engine load,
said control unit being operative to divide said total fuel injection quantity at said determined ratio into injection quantity for first fuel injection and into injection quantity for second fuel injection,
said control unit being operative to determine a first injection timing that falls in a range from the intake stroke to the termination of the first half of compression stroke,
said control unit being operative to determine a second injection timing that falls in the second half of the compression stroke,
said control unit being operative to determine a first pulse width corresponding to the injection quantity for the first fuel injection and a second pulse width corresponding to the injection quantity for the second fuel injection,
said control unit being operative to apply a first fuel injection control signal with said first pulse width, at said first injection timing, to said fuel injector, causing said fuel injector to spray said first injection quantity of gasoline fuel into said combustion chamber, thereby to form a conical ring shaped air/fuel mixture cloud that becomes a circular solid body of mixture as said piston moves from said first injection timing toward a top dead center position of the compression stroke,
said control unit being operative to apply a second fuel injection control signal with said second pulse width, at said second injection timing, to said fuel injector, causing said fuel injector to spray said second injection quantity of gasoline fuel into said circular solid body of mixture, thereby to form, within said circular solid body of mixture, a ring shaped mixture cloud that is superimposed on a portion of said circular solid body of mixture, thereby to establish the cylinder content wherein the density of fuel particles within said superimposed portion is high enough to burn by auto-ignition at an ignition point in the neighborhood of the piston top dead center position of the compression stroke, causing temperature rise and pressure rise, which initiate auto-ignition of the fuel particles within the remaining portion of said circular body of mixture.
In carrying out the present invention, a system for enhanced auto-ignition management in an internal combustion engine is provided, The system comprises:
a cylinder having a cylinder axis thereof;
a cylinder head closing said cylinder;
a reciprocating piston within said cylinder, said piston, said cylinder and said cylinder head cooperating with each other to define a combustion chamber;
intake and exhaust valves for admitting fresh air into said combustion chamber and for discharging exhaust gas from said combustion chamber, respectively;
a fuel injector mounted to said cylinder head and having a nozzle with a spout communicating with said combustion chamber for spraying gasoline fuel into said combustion chamber;
said piston moving along said cylinder axis toward and away from said cylinder head to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in cooperation with said intake and exhaust valves; and
a control unit being operative to establish an engine load threshold and an engine speed threshold;
said control unit being operative to compare the engine load with said engine load threshold,
said control unit being operative to compare the engine speed with said engine speed threshold,
said control unit being operative to enable split fuel injection for auto-ignition combustion in response to the comparing result of the engine load with said engine load threshold and the comparing result of the engine speed with said engine speed threshold,
said control unit being operative to determine a ratio in response to the engine load,
said control unit being operative to determine total fuel injection quantity in response to the engine load,
said control unit being operative to divide said total fuel injection quantity at said determined ratio into injection quantity for first fuel injection and into injection quantity for second fuel injection,
said control unit being operative to determine a first injection timing in response to said engine load such that said first injection timing retards in a direction from the bottom dead center position of the compression stroke to the top dead center position of the compression stroke as the engine load decreases,
said control unit being operative to determine a second injection timing that falls in the second half of the compression stroke, said second injection timing being always nearer the top dead center position of the compression stroke than said first injection timing,
said control unit being operative to determine a first pulse width corresponding to the injection quantity for the first fuel injection and a second pulse width corresponding to the injection quantity for the second fuel injection,
said control unit being operative to apply a first fuel injection control signal with said first pulse width, at said first injection timing, to said fuel injector, causing said fuel injector to spray said first injection quantity of gasoline fuel into said combustion chamber, thereby to form an air/fuel mixture cloud that becomes a solid body of mixture in the vicinity of said cylinder axis as said piston moves from said first injection timing toward the top dead center position of the compression stroke,
said control unit being operative to apply a second fuel injection control signal with said pulse width, at said second injection timing, to said fuel injector, causing said fuel injector to spray said second injection quantity of gasoline fuel into said solid body of mixture, forming, within said solid body of mixture, a mixture cloud that is superimposed on a portion of said solid body of mixture, thereby to establish the cylinder content wherein the density of fuel particles of said superimposed portion is high enough to burn by auto-ignition at an ignition point in the neighborhood of the piston top dead center position of the compression stroke, causing temperature rise and pressure rise, which initiate auto-ignition of the fuel particles within the remaining portion of said circular body of mixture.
In carrying out the present invention, there is provided a method of controlling split gasoline fuel injection for enhanced auto-ignition management in an internal combustion engine, the engine having a cylinder with a cylinder axis thereof; a cylinder head closing the cylinder; a reciprocating piston within the cylinder to define a combustion chamber to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke; intake and exhaust valves for admitting fresh air into the combustion chamber and for discharging exhaust gas from the combustion chamber, respectively; and a fuel injector for spraying gasoline fuel into the combustion chamber, the fuel injector having a hollow cone nozzle with a spout communicating with the combustion chamber, the hollow cone nozzle imparting torque to gasoline fuel passing through the spout, causing the fuel to generate swirl around a spout axis that aligns the cylinder axis, promoting the fuel to spread outwardly along a cone surface of an imaginary circular cone, the imaginary circular cone being a solid cone bounded by a region enclosed in a circle about the cylinder axis and a cone surface that is formed by the segments joining each point on the circle to a point outside of the region and on the nozzle axis within the spout, said method comprising:
establishing an engine load threshold;
establishing an engine speed threshold;
comparing the engine load with said engine load threshold;
comparing the engine speed with said engine speed threshold;
enabling split fuel injection for auto-ignition combustion in response to the comparing result of the engine load with said engine load threshold and the comparing result of the engine speed with said engine speed threshold;
determining a ratio in response to the engine load;
determine total fuel injection quantity in response to the engine load;
dividing said total fuel injection quantity at said determined ratio into injection quantity for first fuel injection and into injection quantity for second fuel injection,
determining a first injection timing that falls in a range from the piston intake stroke to the end of the first half of the piston compression stroke;
determining a second injection timing that falls in the second half of the piston compression stroke;
determine a first pulse width corresponding to the injection quantity for the first fuel injection;
determining a second pulse width corresponding to the injection quantity for the second fuel injection;
applying a first fuel injection control signal with said first pulse width at said first injection timing to said fuel injector, causing said fuel injector to spray said first injection quantity of gasoline fuel into said combustion chamber, thereby to form a conical ring shaped air/fuel mixture cloud that becomes a circular solid body of mixture as said piston moves from said first injection timing toward a top dead center position of the compression stroke;
applying a second fuel injection control signal with said second pulse width at said second injection timing to said fuel injector, causing said fuel injector to spray said second injection quantity of gasoline fuel into said circular solid body of mixture, forming, within said circular solid body of mixture, a ring shaped mixture cloud that is superimposed on a portion of said circular solid body of mixture, thereby to establish the cylinder content wherein the density of fuel particles within said superimposed portion is high enough to burn by auto-ignition at an ignition point in the neighborhood of the piston top dead center position of the compression stroke, causing temperature rise and pressure rise, which initiate auto-ignition of the fuel particles within the remaining portion of said circular body of mixture.
In carrying out the present invention, there is provided a method of controlling gasoline fuel injection for enhanced auto-ignition management in an internal combustion engine, the engine having a cylinder with a cylinder axis thereof; a cylinder head closing the cylinder; a reciprocating piston within the cylinder to define a combustion chamber to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke; intake and exhaust valves for admitting fresh air into the combustion chamber and for discharging exhaust gas from the combustion chamber, respectively; and a fuel injector having a nozzle with a spout communicating with the combustion chamber for spraying gasoline fuel into the combustion chamber, said method comprising:
determining a ratio in response to the engine load;
determine total fuel injection quantity in response to the engine load;
dividing said total fuel injection quantity at said determined ratio into injection quantity for first fuel injection and into injection quantity for second fuel injection;
determining a first injection timing in response to the engine load such that said first injection timing retards in a direction from the bottom dead center position of the compression stroke to the top dead center position of the compression stroke as the engine load decreases;
determining a second injection timing that falls in the second half of the compression stroke, said second injection timing being always nearer the top dead center position of the compression stroke than said first injection timing is;
determine a first pulse width corresponding to the injection quantity for the first fuel injection;
determining a second pulse width corresponding to the injection quantity for the second fuel injection;
applying a first fuel injection control signal with said first pulse width at said first injection timing to the fuel injector, causing the fuel injector to spray said first injection quantity of gasoline fuel into the combustion chamber, thereby to form an air/fuel mixture cloud that becomes a body of mixture in the vicinity of said cylinder axis as said piston moves from said first injection timing toward the top dead center position of the compression stroke,
applying a second fuel injection control signal with said second pulse width at said second injection timing to the fuel injector, causing the fuel injector to spray said second injection quantity of gasoline fuel into said body of mixture, forming, within said body of mixture, a mixture cloud that is superimposed on a portion of said solid body of mixture, fuel particles sprayed at said first fuel injection timing and fuel particles sprayed at said second fuel injection timing coexisting within said superimposed portion, thereby to establish the cylinder content wherein the density of fuel particles of said superimposed portion is high enough to burn by auto-ignition at an ignition point in the neighborhood of the piston top dead center position of the compression stroke, causing temperature rise and pressure rise, which initiate auto-ignition of the fuel particles within the remaining portion of said circular body of mixture.
In carrying out the present invention, there is provided a computer readable storage medium having stored therein data representing instructions executable by an engine control unit to control split gasoline fuel injection for enhanced auto-ignition, the computer readable storage medium comprising:
instructions for establishing an engine speed threshold;
instructions for establishing an engine load threshold;
instructions for comparing the engine speed with said engine speed threshold;
instructions for comparing the engine load with said engine load threshold;
instruction for enabling or disabling split gasoline fuel injection control;
instructions for determining a ratio in response to the engine load;
instructions for determine total fuel injection quantity in response to the engine load;
instructions for dividing said total fuel injection quantity at said determined ratio into injection quantity for first fuel injection and into injection quantity for second fuel injection;
instructions for determining injection timing for first fuel injection; and
instructions for determining injection timing for second fuel injection.